Hormone in Fat Mimics Insulin

Finding may lead to new treatments for diabetes

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THURSDAY, Dec. 16, 2004 (HealthDayNews) -- Japanese researchers have discovered a hormone in abdominal fat that has some of the same characteristics as insulin.

The finding may mean that fat actually has dueling roles when it comes to regulating our metabolism.

A growing body of literature, including this new study, demonstrates that fat secretes hormones. Although this research is preliminary (as is other investigation into the same subject), it may one day hold keys to the treatment of diabetes, an increasingly common disorder around the world.

"The fact that fat secretes hormones has been increasingly obvious over the last several years. Fat all over the body is secreting a whole variety of different hormones that no one ever dreamed of," said Dr. Robert Rizza, president-elect of the American Diabetes Association and professor of medicine at the Mayo Clinic College of Medicine in Rochester, Minn.

"This is a fascinating observation, but it requires considerable additional study," he added.

The finding initially seems counterintuitive, given that more fat in the mid-section -- versus fat under the skin -- is associated with an increased risk of diabetes and other health problems.

"We're finding more and more that fat can be thought of as a hormone-producing organ, and there are both good fat hormones and bad fat hormones," said Dr. Stuart Weiss, clinical assistant professor of medicine at New York University School of Medicine. "Fat hormones let the fat communicate with the rest of the body."

Neither Rizza nor Weiss was involved in the new study, which appears in the Dec. 17 issue of Science.

The authors of the study compared human fat from the abdominal area to fat from under the skin and found that the new hormone, named visfatin, was more plentiful in the abdominal area.

Mouse studies had shown that visfatin behaves somewhat like insulin, the hormone responsible for ushering glucose -- blood sugar -- out of the blood stream. Insulin is a critical player in diabetes and other metabolic disorders. Lack of insulin or the inability of insulin to perform well contributes to the development of diabetes.

Visfatin seems to play a similar role to insulin, although its effect is less powerful. When administered to mice in high doses in earlier studies, it caused a lowering of blood sugar levels. It also bound to insulin receptors to activate the insulin signaling pathway.

There also appear to be differences between the two hormones. Unlike insulin, visfatin levels do not change depending on whether a person is eating or fasting. And visfatin tends to be present in much smaller concentrations, which may account for why it has a smaller effect on blood glucose levels than insulin, the mouse studies found.

Despite the new study's findings, many questions remain about visfatin.

Dr. Iichiro Shimomura of Osaka University and the study's senior author, said in an e-mail interview that high levels of visfatin may contribute to "insulin resistance by continuously stimulating insulin receptors.

"Alternatively, as visfatin activates insulin receptors in a different manner from insulin, visfatin may be useful to treat insulin resistance in people," Shimomura said. A major result of continuous insulin resistance is weight gain.

Asked about the apparent incongruity of having an insulin-like hormone in abdominal fat, Shimomura responded, "That is what we do not know."

Added Weiss: "We don't know the mechanism about how this hormone is controlled and if it's higher or lower in different states of abdominal 'fatness.' Either we need more of visfatin or less of it, depending on the metabolic consequences of high and low levels of the compound. It needs to be characterized and we need to know who has a lot and who has less and what the metabolic consequences are of high levels and low levels."